It has been found that the conventional baking method comprises the steps of treating the surface of the workpiece to cause it not to have weak acidic property and to prevent it from oxidizing, which would otherwise make paint separate from the workpiece, an undercoating treating step for applying a first coating to the workpiece, a heating in a furnace to heat the workpiece from a low to medium temperature, a mobile immersion for applying paint on the workpiece surface, and heating in a furnace utilizing a blast fan, gas or far ultrared radiation to heat the workpiece surface to a temperature above the melting point of the paint, and then cooling of the workpiece.
It should be noted that according to conventional methods, the workpiece first enters into a low temperature region, then a medium temperature and a high temperature region so as to dry the paint film on the surface of the workpiece, and consequently has the following deficiencies:
1. It is necessary to have a lot of equipment for the furnace, thereby increasing the cost.
2. The furnace is increased in length and so it will take a long time for the formation of the product and it will be unfit for mass production.
3. The air transmitted into the furnace contains suspended particles which may dirty the workpiece surface.
4. The paint cannot firmly adhere on the workpiece.
5. The method may present poisoning, pollution and fire accident risks.
6. The energy cost is rather high.
7. The whole installation is too large in volume.
It is, therefore, an object of the present invention to provide an improved method which may overcome the above-mentioned drawbacks.